On 13 Nov 2004 05:59:06 -0500, james <james_at_jdfogg.com> wrote:
> On Sat, 2004-11-13 at 05:13, Tore S Bekkedal wrote:
>> Does anyone know anything about the protocol that the IBM 3270 terminals
>> uses on the BNC ports labelled I/O? Is there any possibility of hooking
>> this up to anything modern?
>
> You mean SNA/SDLC isn't modern? It's at least still very popular. Lots
> of it in use.
I have been away for a time, and am just checking my backlog.
I used to work with 3270-emulation and compatible hardware. Old 3270
controllers did not use SDLC, they were running Basic Mode aka binary
syncroneous. SDLC was an option which came later. This is a synchroneous
protocol without bit stuffing, to obtain binary transparency octets which
were identical to control codes had to be escaped.
IBM 3270 used the EBCDIC control codes for their documented purpose. HP
2645 terminals had an option to run multidropped using an almost identical
protocol. This protocol is half duplex.
>
> I don't remember what the BNC's are for though, but if it's not SNA then
> it might be some kind of video.
>
The coax is used to connect the controller to the terminals. The
controller was connected by modem to the host at speeds up to 19200
bits/s, and controlled a cluster of terminals. The coax protocol was
similar, but used some type of manchester encoding at around 500 kilobaud.
I think Orchid made a PC card with the 3270 coax connector. I believe I
have one hidden away somewhere in my collection.
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Received on Sat Dec 04 2004 - 13:14:23 GMT